Development of the embryo – what you need to know?

Everyone has what is called DNA. DNA is our genetic message that determines all of our physical characteristics; the colour of our skin, hair, eyes, what height we are, the size of our feet etc. Our DNA is decided when we are created, when the sperm has fertilised the egg.

DNA contains 23 pairs of chromosomes, 46 chromosomes altogether.

egg sperm

An egg from a woman’s ovary contains 23 chromosomes and a man’s sperm contains 23 chromosomes. When the sperm and egg join together your DNA is complete and the cell that is created is called an embryo. This new life will then divide and develop in the womb and right up until the child becomes an adult. By then we will have 30 million million cells in our body. Each cell in our body contains the 46 chromosomes, which holds our genetic message in the form of DNA. By looking at just one cell from our body scientists can then know everything about our physical characteristics.

Human Cloning – what you need to know?

For most people they have a unique genetic code; their DNA is different from everyone else’s. However, identical twins share the same DNA and if someone is cloned they may share the same DNA as their clone. DNA determines our physical characteristics but the cloned individual will not be an exact physical copy and everyone has a unique personality as well as unique fingerprints and toeprints.

How cloning works
The method most often used to clone is called cell nuclear replacement.

• The 23 chromosomes in an egg from a woman’s ovary are found in the nucleus of the egg, the centre. In cloning scientists remove the nucleus of the egg so that it is empty.

                               egg egg with nucleus removed

• The person who is going to be cloned has a cell removed from his/her body. This cell contains a complete set of DNA and it is injected into the empty egg. The egg now has a complete set of DNA that is the same as the person who donated the cell; the person being cloned.

                                                 

• A small spark of electricity is then passed through the egg.
  
• The egg is "fooled” by the spark and thinks it has been fertilised by sperm. The embryo then begins to divide and develop, in the same way as any normally created embryo.

What is the difference between so-called therapeutic cloning and reproductive cloning?
So-called therapeutic cloning – a cloned embryo is created and then his/her stem cells are extracted and used for research. Extracting the stem cells destroys the embryo.

Reproductive cloning – the cloned embryo is transferred to a woman’s womb in the hope that he/she will implant and continue development to birth.

Both types of cloning are reproductive because they both reproduce human beings, the only difference is in the way the embryo is treated.

In Vitro Fertilisation (IVF) – what is it and how does it work?

When a couple conceive naturally the egg is fertilised by the sperm inside the woman’s fallopian tube. When a woman has fertility problems the couple might go for IVF treatment. In IVF the sperm and the egg are put together in a glass dish. Once the sperm fertilises the egg the newly created embryo will be allowed to develop for a few days, to check he/she is developing properly. Then he/she is placed into the woman’s womb where hopefully he/she will implant and develop to birth.

When a man has fertility problems scientists use a technique called intra-cytoplasmic sperm injection (ICSI). Scientists puncture a hole in the egg and then the sperm is put on the end of a needle and injected into the egg. Again the newly created embryo will be allowed to develop for a few days, to check he/she is developing properly and will then be placed into the woman’s womb.

Pre-implantation Genetic Diagnosis (PGD) – what is it and why is it used?

PGD is used on embryos created by IVF. Once the embryo is created and has divided into 4 or 8 cells one of his/her cells is removed. Like the cells in our own bodies, the embryo’s cell contains a set of his/her DNA.

Scientists can then study this cell to see if the embryo is carrying any genetic conditions. They can also tell if the embryo is a boy or girl. Some diseases like Duchenne’s Muscular Dystrophy and haemophilia only develop in boys. If a genetic condition is found or if the embryo could develop a sex-related condition then the embryo will be destroyed. If not the embryo may be implanted in a woman’s womb and allowed to grow and develop till birth.

Embryo Experimentation – why is it used?

Embryos are used by scientists for research. What type of research are they used for?

• Research into fertility treatment;
• Research into the causes of genetic disease;
• Research into the causes of miscarriages;
• Research for better types of contraception;
• Research into better ways of finding genetic or chromosome abnormalities in embryos before implantation (see PGD);
• Research into the development of embryos
• Research into serious disease and treatments for serious disease.
  

Human Fertilisation and Embryology Authority (HFEA) –
what is it?

The HFEA was set up by the Human Fertilisation and Embryology Act 1990. Anyone who wants to create embryos by cloning or who wants to create and use embryos for IVF, PGD or embryo experimentation must apply to the HFEA for a license. The HFEA is responsible for making sure that embryos are created and used according to the law.

SPUC Scotland
April 2003
Jacqueline Dalrymple

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